Question re: Pegging using two single-sided dildos

My wife and I have recently started pegging and now I would like to improve her experience. I've looked into double-ended dildos and I guess I'm just not convinced that they are worth it yet. Even with a harness, they all seem to have some flaws. Additionally, I think it's hard to pick a double-ended dildo that has each end satisfy the requirements for both of us. If anyone feels strongly about them, please feel free to convince me otherwise.

As an alternative, I'd like to try using two single dildos. I feel this would be easier to control and we can each select a dildo that fulfills our needs in terms of size, features, etc. My questions:

1. Obviously we would have to use one harness compatible dildo (O-ring in our case). Does the second one have to be harness compatible as well? I imagine that two bases opposed to each other would provide stability but can a regular dildo be used as effectively?

2. Is there an ideal length for the dildo my wife uses? I realize that the answer is dependent on her size, but I was wondering if perhaps shorter or longer worked better in people's experience.

3. Do you think this configuration would work if one or both were vibrating dildos?

4. Rather than a dildo, could my wife use a vibrator? I'm thinking something made in silicone so it has some flexibility.

5. When using a single dildo, we position the base over her clit for stimulation. If we use two single dildos, would we position it the same or base to base? I realize that some harness dildos have a pretty wide base so this may not be much of an issue.

There are several ways of going about this. Some harnesses have both an O-ring and a hole in the pad, and you can use one dildo pointing out (between ring and pad), and one pointing in (between ring and pad, but pointing the other way). This only works if you have an angled dildo for the inside. The Outlaw Leather harnesses do this, as well as some Aslans. Not sure about the SpareParts. Know the Sportsheets harnesses don't.

Some harnesses are specifically designed for this, see the Aslan Double-Up harness (though I'm not exactly sure how it all works).

You can also get something called the Aslan Double-Up Cuff that links two dildos together. There might be other products that do the same thing.